1. Field of the Invention
The present invention relates to a ratchet buckle assembly for tightening a strap for binding a load safely in a desired position in safety, in trucks, cargo-handling installations and the like.
2. Description of the Prior Art
As disclosed in Japanese Patent Laid-Open No. Hei 6-284912, it is well known to construct a ratchet buckle assembly for tightening a binding strap, in a manner such that: a pair of ratchet wheels are fixedly mounted on a strap winding shaft; this strap winding shaft is inserted in an axial hole of a base end portion of each of a main body and a handle; the handle is rotatably connected with the main body; the strap has one of its opposite end portions wound on the strap winding shaft and the other end portion fixed to a strap fixing bar of a front-end portion of the main body; a drive plate, which is slidably mounted in a guide hole, is urged forward toward the ratchet wheels by a compression spring. When the handle is rotated in a predetermined direction, such drive plate is engaged with any one of follower surfaces of teeth of the ratchet wheels, so that the strap winding shaft is rotated in its winding direction, in a condition in which a ratchet slips away along releasing surfaces of the teeth of the ratchet wheels. When the handle is reversed in rotation, the ratchet is engaged with the follower surface of a pair of the teeth of the ratchet wheels to prevent the strap winding shaft from rotating in the reverse direction; and, at the same time, the drive plate is permitted to slip away along the releasing surfaces of the teeth of the ratchet wheels.
In the above-mentioned conventional ratchet buckle assembly: the strap winding shaft is constructed of a tubular element provided with a slot extending in a radial direction of the tubular element; and, the strap has its end portion inserted in such slot, which enables the strap winding shaft to wind the strap thereon.
However, when the strap winding shaft is subjected to an excessively large stress caused by a large tensile force exerted by a random movement of a cargo fixed by the strap, the strap winding shaft is resiliently deformed. When the amount of such shaft deformation exceeds a predetermined limit, the strap winding shaft fails to wind the strap thereon.